U.S. patent number 9,025,921 [Application Number 13/799,736] was granted by the patent office on 2015-05-05 for vibration damper for high power fiber optic transport cables.
This patent grant is currently assigned to BAE Systems Information and Electronic Systems Integration Inc.. The grantee listed for this patent is BAE Systems Information and Electronic Systems Integration Inc.. Invention is credited to Benjamin R. Johnson.
United States Patent |
9,025,921 |
Johnson |
May 5, 2015 |
Vibration damper for high power fiber optic transport cables
Abstract
Embodiments of a method and apparatus for controlling the
mechanical stabilization of an optical fiber are disclosed. The
method may consist of placing an inflatable bladder between an
optical fiber and a protective jacket. The bladder may be inflated
with air, inert gas, or liquid to a desired pressure. The bladder
may be sectioned to extend along part of or the entire length of
the fiber. The bladder may isolate the optical fiber in a periodic
fashion. The temperature of the material inside the bladder may
vary axially along the optical fiber. Embodiments of the invention
can stabilize the optical fiber by providing mechanical isolation
from vibration and other perturbations. Embodiments of the
invention can also alter Stimulated Brillouin Scattering ("SBS")
and Stimulated Raman Scattering ("SRS") thresholds using either
thermal or vibrational perturbations.
Inventors: |
Johnson; Benjamin R.
(Nottingham, NH) |
Applicant: |
Name |
City |
State |
Country |
Type |
BAE Systems Information and Electronic Systems Integration
Inc. |
Nashua |
NH |
US |
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Assignee: |
BAE Systems Information and
Electronic Systems Integration Inc. (Nashua, NH)
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Family
ID: |
51527421 |
Appl.
No.: |
13/799,736 |
Filed: |
March 13, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20140270663 A1 |
Sep 18, 2014 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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61670244 |
Jul 11, 2012 |
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Current U.S.
Class: |
385/100; 385/102;
385/147; 385/104; 385/105 |
Current CPC
Class: |
G02B
6/4429 (20130101) |
Current International
Class: |
G02B
6/44 (20060101) |
Field of
Search: |
;385/100,102,104,105,147 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
http://www.aflglobal.com/Products/Conductor-Accessories/Fiber-Optic-Cable--
Hardware/ADSS-Hardware/Spiral-Vibration-Damper-for-ADSS-Cable.aspx.
2002-2012, AFL, Revision 3, Jul. 23, 2012. cited by
applicant.
|
Primary Examiner: Doan; Jennifer
Attorney, Agent or Firm: Long; Daniel J.
Parent Case Text
CROSS REFERENCE TO RELATED CASE
The present invention is related to and claims the benefit of
priority of U.S. Provisional Patent application No. 61/670,244,
filed on Jul. 11, 2012 and entitled "Vibration Damper for High
Power Fiber Optic Transport Cables."
Claims
What is claimed is:
1. An apparatus for controlling the mechanical stabilization of an
optical fiber comprising: an inflatable bladder located between the
optical fiber and a protective jacket; and a material selected from
the group consisting of air, inert gas, and liquid within said
inflatable bladder, wherein the inflatable bladder acts as a
mechanical dampening medium thereby by providing mechanical
isolation to the optical fiber from vibrational perturbations.
2. The apparatus of claim 1 wherein said inflatable bladder is
inflated via at least one inflation port located on an exterior of
said protective jacket.
3. The apparatus of claim 1 wherein said inflatable bladder is
sectioned to extend along one or more parts of said optical
fiber.
4. The apparatus of claim 1 wherein the temperature of said
material selected from the group consisting of air, inert gas, and
liquid varies axially along said optical fiber.
5. The apparatus of claim 1 wherein said inflatable bladder has an
orientation selected from the group consisting of linear, coiled,
and multiple curves.
6. The apparatus of claim 1 where said inflatable bladder is
directly fastened to said optical fiber.
7. The apparatus of cairn 1 wherein said inflatable bladder is
operated in a static thermal management system.
8. The apparatus of claim 1 wherein said inflatable bladder is
operated in conjunction with a closed loop circulation thermal
management system.
9. The apparatus of claim 1 wherein said inflatable bladder is
placed between said optical fiber and said protective jacket in
periodic installments.
10. The apparatus of claim 9 wherein said material selected from
the group consisting of air, inert gas, and liquid contained in
said periodic installments is of differing temperatures.
11. A method for controlling the mechanical stabilization of an
optical fiber comprising the steps of: obtaining an inflatable
bladder; and placing said inflatable bladder between the optical
fiber and a protective jacket such that said inflatable bladder
exerts even pressure on said optical fiber, wherein said inflate
bladder stabilizes wave guiding properties of said optical fiber by
providing mechanical isolation to the optical fiber from
vibrational perturbations or thermal perturbations.
12. The method of claim 11 further comprising the step of inflating
said inflatable bladder to a predetermined pressure with a material
selected from the group consisting of air, inert gas, and
liquid.
13. The method of claim 11 wherein said inflatable bladder is
sectioned to extend along one or more parts of said optical
fiber.
14. The method of claim 11 further comprising the step of axially
varying the thermal gradient along said optical fiber.
15. The method of claim 11 wherein said inflatable bladder is
operated in a static thermal management system.
16. ne method of claim 11 wherein said inflatable bladder is
operated in conjunction with a closed loop circulation thermal
management system.
17. The method of claim 11 further comprising the step of vibrating
said optical fiber.
18. The method of claim 11 wherein said inflatable bladder is
placed between said optical fiber and said protective) jacket in
periodic installments.
19. The method of claim 18 wherein said material selected from the
group consisting of air, inert gas, and liquid contained in said
periodic installments is of differing temperatures.
20. A apparatus for controlling the mechanical stabilization of an
optical fiber comprising: an inflatable bladder located between the
optical fiber and a protective jacket; a material selected from the
group consisting of air, inert gas, and liquid within said
inflatable bladder, wherein the temperature of said material varies
axially along said optical fiber thereby providing an axially
varying a thermal gradient along the optical fiber; and at least
one inflation port located on an exterior of said protective
jacket.
21. The apparatus of claim 1 wherein the it flat le bladder is
sectioned to extend along an entire length of the optical
fiber.
22. The apparatus of claim 1 wherein the inflatable bladder by
incorporating an active thermal management increases a Stimulated
Brillouin Scattering (SBS) threshold of the optical fiber.
23. The apparatus of claim 20 wherein a Stimulated Raman Scattering
(SRS) threshold of the optical fiber alters by the axially varying
thermal gradient along the optical fiber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high power fiber optic transport
cables, and more particularly to methods and apparatus for
providing mechanical isolation from perturbations impinging on such
cables in harsh environments.
2. Description of Prior Developments
High power fiber optic transport cables are currently protected
with Kevlar reinforced plastic jacketing and flexible metal armored
cables. Such protection is effective at providing mechanical
protection from environmental stresses, but ineffective at
providing consistent mechanical stabilization along the length of
the optical fiber in high power fiber optic transport cables.
Mechanical stabilization is required in the new generation of large
core (>20 um), single mode optical fibers such as Leaky Core
Fibers, Chiral Coupled Core Fibers, High Order Mode Fibers, and
Large Mode Area Fibers. Mechanical perturbations on these new
fibers can disrupt the fiber's ability to propagate the optical
field in a single mode along the entire length of the fiber. This
results in inadequate beam quality, inconsistent optical
performance, and unstable power transmission. Thus, the protection
of high power fiber optic transport cables still has many needs for
which a solution is required.
Need for Modal Quality
As fiber lasers and amplifiers increase in power the need for
larger core optical fibers that operate in the high brightness,
single transverse mode regime increases. This has pushed the
optical fiber industry to develop unique fiber geometries and
unique wave guiding strategies that coerce an optical fiber into
single mode operation despite basic physics principles dictating
otherwise. The Large Core Optical Fibers (LCOF) under discussion
are known as Large Mode Area (LMA), Chirally Coupled Core (CCC),
High Order Mode (HOM), and Leaky Core Fibers (LCF). The ability of
these fibers to transmit, or propagate, the optical power in a
single transverse mode depends highly on the mechanical stability
of the fiber. The delicate conditions required for single mode
propagation are easily disrupted in environmentally demanding
applications such as those, for example, on military aircraft.
Single transverse mode operation in LCOFs is achieved via
differential mode loss of higher order modes from the fiber optic
core to the surrounding cladding or a secondary core structure. The
modal phase matching characteristics of LCOFs that encourage
efficient coupling of higher order optical modes into the cladding
of the optical fiber depend highly on the mechanical stability of
the fiber. Mechanical perturbations disrupt such conditions and
therefore prohibit efficient single mode operation of large core
optical fibers. Under transient conditions the degree of higher
order mode coupling into the cladding can differ along the length
of the fiber and vary temporally. The temporal fluctuations lead to
variations in optical power and gross degradations in beam quality
and optical brightness. The degradation in single mode performance
of LCOF fibers is greatly exacerbated when fiber lengths exceed
several meters in length.
Need for Stable, High Extinction Polarization
The polarization stability of polarization maintaining (PM) LCOFs
also depends on the mechanical stability of the fiber. Mechanical
perturbations on PM fibers disrupt the intrinsic birefringence of
the fiber that provides the designed polarization stability. The
disruption arises from the photoelastic effect where the refractive
index of an optical glass is dependent on the mechanical stress it
is under. When periodic (or randomly distributed) vibrations
impinge PM optical fiber, temporal fluctuations of polarization
quality (degree of linear polarization, polarization orientation)
occur. This is detrimental for applications such as nonlinear
frequency conversion, or wavelength shifting using Stimulated Raman
Scattering ("SRS"), or other applications requiring stable, highly
polarized energy.
Need for Stable Power and High Brightness
High optical brightness is often required in military applications
utilizing lasers, particularly in IRCM and Target Designation
applications. The brightness of a source depends on the absolute
power/energy of the source and the size of the desired spot on the
"target." On military platforms, for example helicopters, the
source and output are often remotely located--requiring the need
for optical transport cables. As the brightness requirements of
such applications increases, the absolute optical power is
increased. The increased power requirements push the material
limits of current optical fiber technology, requiring the
implementation of above mentioned LCOFs in such applications. This
naturally leads to an application conflict where the required
product is inadequate or less than ideal. Under vibration the
current LCOFs will exhibit fluctuations in power due to
differential mode coupling differences along the length of the
fiber. This results in a lower brightness beam with temporally
inconsistent power.
Need for Increased SBS Threshold
Single wavelength lasers, or very narrow bandwidth lasers, of
significant powers (>10 W), particularly when pulsed to higher
peak powers, are limited in applications utilizing optical fibers
due to the nonlinear process known as Stimulated Brillouin
Scattering ("SBS"). SBS is an inelastic scattering process that
couples energy from a "pump" wave into a lower energy "signal"
wave, or an anti-stokes wave, via spatial phase matching by a
pump-generated, counter propagating acoustic phonon. This threshold
is both material dependent and dependent on the geometrical
properties (waveguide area, shape, length) of the waveguide and
propagating beam. The threshold for SBS is generally low in single
frequency fibers and results in a gross limiting of output power
from the laser.
Need for SRS Alteration
Several wavelength shifting architectures use SRS to generate
wavelengths that are not readily accessible by common solid-state,
fiber, gas, dye, or diode lasers. Raman scattering is an inelastic
scattering process where the energy from a optical "pump" wave to a
"signal" wave, or stokes wave, occurs via optical coupling through
a co-propagating optical phonon. The emitted signal wave is lower
in energy by a material dependent energy constant. SRS is a process
that is both desired and avoided in fiber lasers and amplifiers
depending on the application. Many telecom amplifiers use SRS,
known as Raman Amplifiers, to amplify optical energy in a broad
frequency spectrum. Some high power fiber lasers exploit SRS to
frequency shift light from a pump frequency to a desired frequency.
Conversely, in some high power fiber lasers, SRS is avoided due to
the transfer of energy from one frequency to an unwanted frequency.
This is all application dependent.
In sum, there is a need for an invention to improve degradation of
beam quality, polarization instability, decreased brightness, and
power transmission inefficiency in high power, fiber optic
transport cable assemblies in harsh environments. There is also a
need for an invention to provide preferential enhancement or
mitigation of nonlinear fiber optic processes, such as SRS or
SBS.
SUMMARY OF THE INVENTION
Embodiments of the present invention may provide a solution to
these needs by providing mechanical isolation from perturbations
impinging on a high power fiber optic transport cable in harsh
environments. In one embodiment, this isolation may be performed by
providing a mechanical buffer between the optical fiber and the
protective jacketing in the form of a symmetric, inflatable bladder
that exerts even pressure on the optical fiber. The mechanical
buffer may consist of a concentric, extruded bladder with inflation
ports located on the exterior of the armored jacket. The concentric
bladder can be inflated to a desired pressure with an engineered
gas or fluid to provide a custom tailored isolation profile. The
bladder may be implemented in a static system or a closed loop
circulating system to provide active thermal management.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention, as well as a preferred mode of use,
further objects, and advantages thereof, will best be understood by
reference to the following detailed description of an illustrative
embodiment when read in conjunction with the accompanying drawings,
wherein:
FIG. 1 shows a cross section view of an isolation bladder before
and after inflation.
FIG. 2 shows a side view of an armored transport cable with an
isolation bladder.
FIG. 3 shows a side view of a periodic bladder configured, for
example, for SBS suppression or SRS enhancement.
FIG. 4 shows an isolation bladder configured for active thermal
management.
FIG. 5 shows an axially segmented bladder configured, for example,
to create an axially varying thermal gradient.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Referring now to the drawings, FIG. 1 shows a cross-section view of
a symmetric, inflatable bladder 102 located between an optical
fiber 104 and an armored jacket 106 both before and after
inflation. The bladder 102 may exert an even pressure on the
optical fiber 104. The bladder 102 may stabilize the wave guiding
properties of the optical fiber 104 by providing mechanical
isolation from vibration and other perturbations. The bladder 102
may be inflated with air, inert gas, or a fluid via an inflation
port 108, and may provide an engineered thermal or vibrational
perturbation to disrupt the acoustic wave guiding properties of the
optical fiber 104. This may increase the threshold of Stimulated
Brillouin Scattering ("SBS"). Additionally, the bladder 102 may
alter the threshold for Stimulated Raman Scattering ("SRS").
The bladder 102 can provide a mechanical dampening medium that is
easily customizable according to the demands of the application.
The bladder 102 may be oriented linearly, coiled, or in multiple
curves conforming to a routing surface. The bladder 102 may also be
fastened to a vibrating surface directly.
Embodiments of the present invention can both preserve the high
order coupling of LCOFs and the single mode operation of LCOFs.
Embodiments can also stabilize the degree of linear polarization
and preserve the orientation of the light in LCOFs.
FIG. 2 shows a side view of the bladder extending along the length
of the fiber. The bladder may be sectioned or extruded to extend
along part of or along the entire length of the fiber.
Embodiments of the present invention may increase the SBS threshold
by disrupting the propagation of the acoustic wave within the
optical waveguide. The mechanical disruption can be in the form of
a thermal or vibration perturbation that essentially destroys the
acoustic waveguide properties of the optical waveguide. As shown in
FIG. 3, in one embodiment, the acoustic wave may be disrupted by
vibrating the transport cable while partially isolating the fiber
with periodic bladders 302. If the periodic structure is employed,
the periodic bladders 402 may contain fluid or gas that is of
differing temperatures that subsequently disrupt the acoustic
wave.
Embodiments of the present invention may alter the SRS or SBS
threshold providing active thermal management to the bladder. FIG.
4 illustrates one process by which such active thermal management
may be accomplished. Embodiments of the present invention may be
operated in either a static thermal management system or in
conjunction with a closed loop circulation thermal management
system.
Referring now to FIG. 5, embodiments of the present invention may
alter the SRS threshold by providing an axially varying thermal
gradient along the fiber. This axially varying thermal gradient may
alter the index of refraction of the optical fiber and its
intrinsic ability to host the phase matching optical phonon
consistently along the length of the fiber; a condition that is
critical for energy transfer to occur. The specificity of the
thermal gradient may determine whether the threshold is increased
or decreased.
While the present invention has been described in connection with
embodiments of the various figures, it is to be understood that
other similar embodiments may be used or modifications and
additions may be made to the described embodiment for performing
the same function of the present invention without deviating
therefrom. Therefore, the present invention should not be limited
to any single embodiment, but rather construed in breadth and scope
in accordance with the recitation of the appended claims.
* * * * *
References